Our preliminary studies show that canine endothelial cells mechanically harvested from segments of autogenous veins may be seeded onto prosthetic arterial grafts, resulting in a cellular luminal surface that meets all the standard histologic, ultrastructural and immunological criteria for endothelium and has resistance to clotting similar to that of endothelhum. These are studies to characterize the process by which seeding leads to the endothelial lining and to determine the cell of origin of that lining. In addition, we will examine the alternate means of harvesting cells in order to obtain the greatest number from the smallest segment of vein and, subsequently, compare the completeness with which these methods line arterial prosthetic grafts. In order to identify elements of graft construction that favorably affect seeding, we will test the facility with which this lining may be seeded onto grafts representative of the spectrum of materials currently in clinical and experimental use. Methods for producing grafts fully lined with endothelium in tissue culture will be developed and applied to the problem of patency in small arterial substitutes. Although all studies will be done in dogs, we hope that the techniques may become applicable to the use of vascular prostheses in humans.